The present invention relates to a large returnable (refillable) container, a method of molding a large returnable container, a large returnable container molding apparatus, and a blow mold having separate heating zones.
A large returnable container having a large capacity (e.g., 3 or 5 gallons (about 20 liters)) is collected from the market, refilled, and reused. A large returnable container has been widely used as a drink container (e.g., mineral water container). It is necessary to wash a used container with alkaline hot water or the like at a temperature of 60 to 70° C. before refilling the container with a drink.
A large returnable container has been produced by injection-molding a polycarbonate (PC) preform, and blow-molding the preform (see JP-A-8-164557).
In recent years, it has been pointed out that elution of a bisphenol A component may occur when a synthetic resin produced using bisphenol A as a raw material (e.g., polycarbonate or epoxy resin) is washed with a powerful cleaner, or comes in contact with an acid or a high-temperature liquid. Therefore, an alternative to polycarbonate has been desired as a material for forming a large returnable container.
An alternative to polycarbonate has also been desired from the viewpoint of product cost. Specifically, polycarbonate has high transparency, heat resistance, impact resistance, and quality, but is expensive. It has been proposed to produce a large returnable container using an inexpensive polyester resin such as polyethylene terephthalate (PET) instead of polycarbonate (PC) (see JP-A-11-34152).
A blow molding method that provides heat resistance to a small or medium-sized container having a capacity of several liters or less (e.g., 500 cc to 2 liters) has been known. Specifically, a primary blow-molded article obtained by subjecting a preform to primary blow molding, or a secondary blow-molded article obtained by subjecting the primary blow-molded article to secondary blow molding, is subjected to a heat treatment, and the resulting intermediate molded article that has been thermally shrunk is subjected to final blow molding to obtain a heat-resistant container (see JP-A-10-286874, JP-B-3777204, JP-A-2006-117289). The degree of crystallinity can be improved and a strain that has occurred during stretch orientation by subjecting the stretch-orientated container to a heat treatment is removed, so that the heat resistance of the container is improved.